30CrMnSiA支臂零件裂纹产生原因分析

30CrMnSiA支臂零件在机加工和热处理后，经无损探伤检验发现在零件轴线多处有裂纹存在。为明确支臂零件裂纹产生的原因，通过宏观观察、金相组织分析、微观观察和能谱分析、力学性能测试、化学成分分析等试验手段进行分析，并与原材料进行对比。结果表明:该零件材料的微观组织不均匀，容易产生较大的组织应力，异常的带状组织分布方向与裂纹扩展方向一致；裂纹主要位于零件截面尺寸变化处，因筋条的尺寸变化而造成的淬火冷速不一致，导致裂纹处存在较大热应力。经分析可知，零件裂纹均为淬火裂纹，零件原材料带状组织不均匀和零件形状尺寸变化较大等综合因素导致该零件淬火时容易产生淬火裂纹。

Analysis of Crack Causes of 30CrMnSiA Arm

After 30CrMnSiA arm parts undergo machining and heat treatment, it is found that there are many cracks in the axis of the parts through magnetic particle inspection. In order to find out the cause accounting for the crack in the arm parts, in this work, macroscopic observation, metallographic structure analysis, scanning electron microscope and energy spectrum analysis, mechanical properties analysis, chemical composition analysis ect. were conducted and compared with that of the pristine one. The results show that the microstructure of the part is not uniform, resulting in large stress. The distribution direction of the abnormal banded structure is consistent with the crack propagation direction, and the cracks are located at the dimensional change of the cross section part. As the quenching cooling rates are different due to the variable rib sizes, there are high thermal stress at the cracks. Analysis results illustrate that all the cracks of the parts are quenching cracks. The comprehensive factors such as the uneven banded structure of the raw materials and the significantly varied shapes lead to the quenching cracks of the parts.